Films extruded from high density polyolefins, especially high density polyethylenes, have become an important product worldwide. Even more particularly, the use of multimodal or bimodal polyethylenes in films has gained market share over traditional unimodal polyethylenes. An example of producing high density films can be found in U.S. Pat. No. 6,878,454. In order to make such films, complex reaction processes such as the use of multi-site catalysts and/or multi-stage reactors are necessary. This can often lead to problems in the quality of the film, such as the presence of gels. The formation of gels in films is well known in the art and can be characterized as highly localized imperfections in the film that are visually distinct from the surrounding film, mostly due to the presence of either high concentrations of unblended polymer, unreacted catalyst and activator, or both, but can include other types of visually distinct imperfections as well. The presence of gels lowers the value of these films, and in some cases makes the films unmarketable.
It has been found by the inventors that the way in which the activator is added to the reactor can influence the final properties of the polyolefin that is produced in the reactor, and the films extruded therefrom. There have been various disclosures that describe alternative means of adding catalyst components such as the catalyst activator to polymerization reactors, such as in U.S. Pat. No. 4,287,327, U.S. Pat. No. 4,665,143, U.S. Pat. No. 5,290,745, U.S. Pat. No. 5,541,270 and U.S. Pat. No. 6,306,981. To date, there has been no solution to the problem of improving the properties of the films generated from high density polyolefins. The present invention is directed to an improved method of forming films from high density polyolefins.